Process for manufacturing iron or steel with low sulphur content



Feb. 11, 1969 c. F. NIEHAUS 3,427,150

PROCESS FOR MANUFACTURING IRQN OR STEEL WITH LOW SULPHUR CONTENT Filed Aug. 9, 1966 Feb. 11, 1969 c. F. NIEHAUS 3,427,150

PROCESS FOR MANUFACTURING IRON OR STEEL WITH LOW SULPHUR CONTENT Filed Aug. 9, 1966 Sheet 2 of 2 United States Patent 3,427,150 PROCESS FOR MANUFACTURING IRON OR STEEL WITH LOW SULPHUR CONTENT Conrad F. Niehaus, Johannesburg, Transvaal, Republic of South Africa, assignor to Niehaus Engineering S.A., Fribonrg, Switzerland Filed Aug. 9, 1966, Ser. No. 571,287 Claims priority, application Switzerland, Aug. 19, 1965,

11,685/ 65 US. C]. 7555 1 Claim Int. Cl. C21c 7/02 ABSTRACT OF THE DISCLOSURE This invention relates to the production of iron or steel.

In the production of pig iron in a blast furnace or the like the raw ore is introduced into the furnace together with coke for combustion and other purposes. The coke is the cause of sulphur being introduced into the iron bath which develops at the bottom of the furnace and sulphur is generally an unwanted constituent in iron or steel, at least when present in significant quantities. To remove sulphur a slag forming agent such as calcium carbonate is added.

The addition of slag forming agents sets up a circular reaction which in the result affects the output capacity of a blast furnace. For instance, to de-sulphurize the molten iron in the furnace lime is necessary and this substance has to be melted. Thus the coke has the double task of reducing the iron ore and heating up the lime. If additional lime is required to remove at least some of the sulphur trapped in the molten metal then further coke is required to melt this additional lime. The excess coke and lime adds to the cost of melting an ore batch. Further, the excess coke and lime required reduces the furnace space available for producing pig iron. The economies of blast furnace operations are such that the removal of the sulphur down to very low limits in these vessels is impractical, at least in the experience of the applicant. Consequently, in general practice the steel produced in a converter has a sulphur content which is largely dependent on the product of the blast furnace and as a rule this is higher than desirable. The comparatively high sulphur content in the final steel product is a necessary result of the economic dictates governing the operation of the blast furnace. Of course, for special quality steels other considerations will apply.

An object of the present invention is to provide a method of de-sulphurizing steel and iron which the applicant believes will have several useful advantages, especially in regard to the economies of blast furnace operations.

According to the invention a method of de-sulphurizing iron or steel includes the steps of locating the metal in molten state in a vessel, adding a slag forming de-sulphurizing agent to the metal and causing at least some of the agent to move continuously in a path through the metal which ensures that substantially all the metal is brought into contact with the agent.

Further according to the invention the movement of the agent is effected by generating opposed wave trains in at least the surface region of the molten metal which merge to define a central disturbance in the metal, the

3,427,150 Patented Feb. 11, 1969 central disturbance acting to project the agent deep into the molten metal mass.

Preferably the agent is caused to radiate outwardly toward the sides of the vessel after it has been projected into the metal mass, thereafter to move upwardly in the vessel against the side walls thereof.

The invention also visualizes the use of a de-sulphurizing agent which also serves for de-phosphorizing and decarborizing purposes. One such agent would be calcium oxide.

Also according to the invention the vessel is characterized in circumferentially spaced opposed side wall zones of different diameters, and movement of the agent in the metal mass is effected by rotating the vessel about an axis passing centrally through the vessel and inclined to the horizontal.

The agent projected into the metal mass may be caused to move radially outwardly from the center over upwardly sloping floor zones of the vessel towards the side of the vessel.

In order to illustrate the invention an example is described hereunder with reference to the accompanying drawings in which:

FIGURE 1 is a schematic arrangement of apparatus employed in the exercise of the method.

FIGURE 2 is a vertical section through a converter in which the method is exercised, the section showing the agitation in the vessel passing through a positive half wave in the central surface region.

FIGURE 3 is a section similar to that of FIG. 2 with the agitation in the vessel passing through the negative half wave in the central region, and

FIGURE 4 is a plan view of the converter showing the wall formation needed to effect the desired agitation.

Referring to FIGURE 1, raw iron ore passes into the blast furnace 5 in the direction of arrows 6. Coke for combustion purposes and slag forming agents such as calcium carbonate are also added to the blast furnace in the direction of arrows 6. The coke acts to supply the heat for reducing the iron oxide to molten iron and the molten iron drips through the slag bed to form a bath at the base of the furnace. The action of the calcium is to de-sulphurize the molten metal.

The molten metal is taken from the blast furnace through the discharge through 7, the metal falling in the direction of arrows 8 into the vessel 9. Vessel 9 is then employed to convey the molten metal to the bath 10 which is in the nature of a storage reservoir. From the storage reservoir charges of molten pig iron are withdrawn for passage in the direction of arrows 11 to the converter 12.

Converter 12 is characterized in a section as shown in FIGURE 4, namely two opposed curved walls 13 and two opposed fiat walls 14. In addition the base or floor 15 of the converter is equipped with sloping sections 16. The converter is adapted to be rotated at an inclination to the horizontal through suitable rotating means 17 (FIG. 1).

In the arrangement under consideration the flat and curved side wall zones act to set up in a bath of molten metal in the vessel trains of opposed waves which merge to create in the central surface region of the bath a mixing agitation. Under resonating circumstances these opposed wave trains may be caused to merge into a single wave 18 (FIG. 2) of substantial amplitude and this is probably the ideal state for the de-sulphurizing of the molten metal.

Calcium oxide is added to the metal bath in the converter and the slag formed thereby is not permitted to rest as a layer on top of the molten bath. Instead the mixing action in the bath acts to break up the slag layer and particles of slag are caused to move through the bath in the directions of arrows 19 as shown in FIGURES 2 and 3. In consequence the calcium oxide, which acts as a de-sulphurizing agent, is projected into the metal bath so that little if any of the metal is not brought into contact with the calcium oxide. By this means an efficient use is made of the CaO as a de-sulphurizing agent. In conventional converters the de-sulphurizing agent is not given much opportunity to attack the sulphur in the metal which is comparatively removed from the slag layer.

Simultaneosuly with the de-sulphurizing activity in the converter de-phosphorizing and de-carborizing may take place. In FIGURE 1 element 20 is an oxygen lance.

The method of the invention sets out to render it possible to operate blast furnaces under existing circumstances without too much concern about the sulphur content of the pig iron produced therein. The amount of sulphur in pig iron issuing from a blast furnace can be controlled to suit requirements but an eye has always to be kept on the economies of the process. Considerable quantities of coke and slag forming agents are necessary to yield a pig iron having a sulphur content as low as, say, 0.04% and thereafter the reduction of this percentage below 0.02% in a conventional converter is by no means easy.

With the present invention test runs have shown that it is possible to take an iron from a blast furnace with a sulphur content in the region of 0.1% and to convert this iron into steel with a sulphur content of less than 0.02%. And these figures indicate that the weight of calcium carbonate in the shaft or blast furnace can be reduced to about 20% of the weight of the pig iron formed in the furnace while the slag increase in the converter is of the order 58%.

Further de-sulphurizing in the converter was achieved without any consequential heat losses during oxygen blowing and without any material increase in the blowing time.

In a test the actual sulphur content of the steel produced in the converter from pig iron having a sulphur content of about 0.125% was lower than 0.01% and de-sulphurizing was achieved before de-carborizing had proceeded to completion.

Many more examples of the invention exist each differing from the other in matters of detail only. The essence of the invention is the de-sulphurizing of pig iron in a rotating converter by causing the slag to be moved in currents through the molten metal bath located in the converter. The de-sulphurizing agent is forced to move through the metal mass instead of lying substantially on the surface thereof. It will be clear that the high amplitude of wave 18 will ensure that during the negative half wave particles of de-sulphurizing agent are projected deep into the metal bath. These particles will then radiate outwardly to the region of the sloping floor zones 16 where they will be caused to move upwardly along the side walls of the converter. The wave trains generated in the molten mass act to project the particles radially inwardly towards the central high peak of wave 18. The angle of operation of the converter is a matter to suit circumstances. Obviously the effective capacity of the converter will increase the nearer the converter operates to the vertical What I claim is:

1. A method of de-sulphurizing ferrous material including the steps of locating the metal in a molten state in a vessel, adding a slag forming de-sulphurizing agent to the metal, and simultaneously generating opposed wave trains in at least the surface region of the molten metal which merge to define a central disturbance in the metal, the central disturbance acting to project said agent deep into the metal in a path which splits to permit said agent to radiate outwardly towards the side walls of the vessel and generally to create currents in said path of figure 8 form in the vertical section said wave trains being generated by rotating the vessel about an axis passing centrally through the vessel and inclined to the horizontal.

References Cited UNITED STATES PATENTS 2,902,358 9/ 1959 Kalling et al. 60 3,136,626 6/1964 Decamps 7552 3,172,756 3/1965 Bengtsson 7552 3,259,486 7/ 1966 Kootz et al 7552 3,326,672 6/ 1967 Worner 7552 3,334,993 8/1967 Nojima -1 7545 RICHARD O. DEAN, Primary Examiner.

US. Cl. X.R. 7552, 61 

